1. Field of Endeavor
The present invention relates to the field of turbines, and to a rotor blade arrangement.
2. Brief Description of the Related Art
Blades for gas turbines, which are used in the compressor section or turbine section as stator blades or rotor blades, are customarily produced as one component by forging or precision casting. This especially also applies to blades which have a platform and/or a shroud segment.
The increase of efficiency and performance of modern gas turbine plants, which is necessary for environmental protection reasons, requires raising the hot gas temperature and reduction of the cooling air consumption (active cooling and leakage). Consequently, the loading of stator blades and rotor blades is inevitably increased. This can be counteracted, inter alia, by material developments and coating developments. There is another possible way of reducing stresses by constructional measures. With the same service life, components with reduced stress can endure higher temperatures. In this way, the requirement for higher hot gas temperature and lower cooling air consumption can be partially taken into consideration.
For reducing stresses on the blades, it has already been proposed to construct stator blades from individual components (outer and inner platforms and blade aerofoil) and to fit them in gas turbines (see for example U.S. Pat. No. 5,494,404 or U.S. Pat. No. 5,564,897 or EP-A2-1 176 284). The individual components of the blade in this case can be connected either in a form-fitting manner or by brazing or welding. In the one case, additional sealing joints are created. In the other case, deformations are transmitted between the components. Stator blades, however, are exposed to different loads than rotor blades because the centrifugal forces which are created as a result of the rotation of the machine are not applied in the case of stator blades.
It is furthermore known, in the case of rotor blades, to fit separate platforms as intermediate pieces between adjacent blades in the rotor (see WO-A1-2007/012587 or DE-A1-199 40 556). As a result of the decoupling of deformations from platform and blade aerofoil, lower stresses are created.
It has also been proposed (US-A1-2006/0120869) to construct a rotor blade from a multiplicity of individual blade elements, wherein the blade aerofoil is assembled from a core and a shell which encloses the core, and the core is anchored in a fixed manner in a blade root, a (lower) platform being formed on the blade root at the same time. As a result of this, a blade aerofoil and platform can, it is true, be decoupled with regard to deformations. However, the complex construction of the blade and the multiplicity of additional sealing joints which are associated with it, which in this case can also lead to increased leakage, is disadvantageous. In this case it is especially also disadvantageous that the forces which act on the blade aerofoil are not introduced directly into the blade carrier but via the blade root which is provided with the platform.
A method for producing a rotor blade is known from U.S. Pat. No. 6,331,217, in which individual blade segments are cast from a superalloy and then interconnected in a materially bonding manner by “Transient Liquid Phase (TLP) Bonding”. In this case, it is true that sealing joints are dispensed with. The decoupling between the segments, however, is low or even non-existent and the method is very costly.
EP 0 764 765 discloses a blade having an airfoil and a platform element made in two separate pieces. During operation, the centrifugal forces press the sides of the platform element against the airfoil element to get a strong coupling.
U.S. Pat. No. 5,378,110 discloses a compressor rotor having the platforms integrated into the rotor and strongly connected to airfoils.
EP 1 306 523 discloses airfoils connected to a rotor through Ω elements that prevent their pivoting. During operation, centrifugal forces press the sides of the Ω elements against the sides of the airfoils realizing a strong coupling.
DE 437 049 discloses turbine blades with T-shaped foot and spacers (defining the platform elements) to connect the blade to a blade carrier. Through this type of connection a strong coupling between blades and spacers is obtained.